The invention is directed generally to a lens arrangement, and more particularly, to a lens arrangement for use with a light distribution and detection apparatus, which apparatus is preferably utilized in connection with a device for determining a location of an object within a given target zone.
While the lens arrangement of the invention is useful in a variety of applications, the disclosure will be facilitated by specific reference to use thereof for distributing light in a device for determining the location of an object within a target zone. One such device is disclosed as an "optical touch screen input device" in U.S. application Ser. No. 492,859, filed May 9, 1983, now U.S. Pat. No. 4,553,842 which application is assigned to the assignee of the present application.
As more fully described in the above-referenced application, such touch screen input devices are generally utilized with cathode ray tubes or other type of visual display screens or elements which are utilized with many computers and computer terminals for example. Such touch screen input devices include screen overlays superimposed upon the display screen, which may be of a capacitive or resistive type or alternatively may be ultrasonic or consist of a conductive grid. However, as described in the above-referenced application, such an overlay may also comprise an optical apparatus which generally creates a "light curtain" in front of the display screen, preferably in the non-visual infrared range so as not to interfere visually with reading of the screen by the operator. Penetration of this light curtain by an object, such as the finger of an operator, a pencil, or the like is readily detectable by the touch screen input apparatus and is interpreted to fix the location of penetration of the object relative to the touch screen and hence relative to the display screen.
In the optical touch screen input apparatus described in the above-referenced patent application, a generally rectilinear frame defines a generally rectangular target zone. A light distribution and detection apparatus mounted at one corner of the frame directs light into this target zone. Reflective assemblies extend along three sides of the target zone and are arranged to reflect light incident thereupon back to the light distribution and detection apparatus for detection thereby. A detector portion of the apparatus or device is associated with a scanning assembly which scans the target zone for receiving the return beams of light therefrom. Hence, a determination of the angular position of the scanning assembly at any given point in time also determines the angular orientation of the path of return light incident at that same time upon the detector.
The presence of an object in the target zone will result in a marked decrease in the amount of light reflected at angular orientations corresponding to the position of the object. The reflective assemblies are positioned so as to cause light to be received at the detector from at least two angular orientations with respect to any given point on the screen during the screening thereof. Hence, any object within the target zone will cause a marked decrease in received light at the detector for each of at least two angular orientations covered by the scanning process. Upon determining the two angles at which this decreased return light energy is detected, the position of the object relative to the two dimensions of the display screen may readily be determined.
While the foregoing apparatus and system has found widespread acceptance, there is room for yet further improvement. For example, in optical systems of this type there is always the problem of light losses which losses detract from the net amount of light reaching the detector. To maximize the sensitivity and resolution of the optical touch screen device, it is generally desirable to maximize the net amount of light energy available in the device. This also enhances the contrast between reflected light reaching the detector directly and light blocked by the object which is to be detected. These losses become particularly problematic as the size of the target zone increases.
In this latter regard, for relatively large display screens or devices, correspondingly large optical touch screen input devices are required. However, the problem of adequate illumination of a target zone becomes more acute as the size of the target zone correspondingly increases. While it is possible to utilize correspondingly higher intensity light sources, such light sources are also significant sources of heat energy, and this heat energy must be dissipated in the device. Any build-up of heat energy can cause significant other problems with the detection apparatus and other portions of the optical touch screen device. While specialized elements and components for operation at higher ambient temperatures may be utilized, this adds a significant expense to the apparatus. Alternatively, heat dissipation apparatus such as fans, heat sinks, cooling fins or the like may be added, but this also adds considerable expense to the apparatus. However, in many light distribution and detection devices heretofore associated with optical position locating or touch screen devices, little if any effort has been made to direct or focus the maximum amount of available light energy from the light source to the target zone. Accordingly, it is a general object of this invention to provide novel apparatus for increasing the proportion of light from the light source reaching the target zone, which will be appreciated to be particularly advantageous in connection with position locating devices utilizing relatively large target zones.